EUV source gets ready for market

26 May 2004

German firm Microliquids is developing an extreme ultraviolet (EUV) source using its laser driven liquid jet technology

German spin-off Microliquids has told Optics.org that it aims to have an extreme ultraviolet (EUV) source based on liquid jet technology on the market next year. Its 13.5 nm source could be a hit with semiconductor manufacturers looking to develop a next generation lithography platform. The young start-up was founded in July 2003 by a small group of scientists from the Max-Planck-Institut für Strömungsforschung, the Max-Planck-Institut für biophysikalische Chemie and the University of Göttingen.

EUV sources, with a target wavelength of 13.5 nm, will be required in the future to create more powerful computer chips. Moving from today’s excimer wavelengths of 193 and 248 nm to shorter EUV wavelengths allows the lithography of smaller IC features required for faster processors and higher memory density.

However, there are significant challenges to overcome. EUV is absorbed by both air and traditional lenses and so the optics must be vacuum based. In addition, the wavelength must be very tightly controlled to match the sophisticated system of mirrors that would be needed to project chip patterns on to the wafers. As a result, EUV lithography requires a high power and narrow waveband source that suits a production environment.

The firm’s prototype EUV source works by irradiating a thin thread of liquid Xenon, 10 to 100 µm in diameter, with a pulsed 2 W Nd:YAG-laser (532 nm) to create a plasma which then emits radiation at 13.5 nm. The system is currently under test to measure its output power.

“The advantage is that it is a real point source radiating in all directions,” company spokesman Tim Spangenberg told Optics.org. “This makes it easier to focus, compared with discharge plasmas which are ellipsoidal.” Laser based plasmas are also expected to produce higher EUV output than their discharge based rivals owing to superior conversion efficiency (see OLE October 2003).

By varying the target medium, Microliquids says that wavelengths of between 2 and 20 nm can be generated which potentially allow the creation of ICs ten times smaller than those presently made.

Xenon gas is cooled to form a liquid and then passed though a nozzle under high pressure (5 to 50 bar) to create a thin thread. Depending on the liquid the thread can be stable along a length of up to 100 mm, even in vacuum.

Microliquids currently provides laser driven liquid gas sources in vacuum for a range of applications including lithography, and is actively seeking partners to develop a complete EUV source.

Author
James Tyrrell is reporter on Optics.org and Opto & Laser Europe magazine.